1. Field of the Invention
The present invention relates to a power distribution apparatus mounted on a vehicle (or the like) to distribute an electrical power to a variety of electrical loads in the vehicle.
2. Description of Related Art
In the conventional vehicle adopting a power source part of 14V (voltage), the power distribution apparatus includes an electrical connection box to which high-voltage power is supplied from the power source part, and a plurality of electronic control units connected to the electrical connection box through power lines, the electronic control units each having a built-in series regulator to which the high-voltage power is distributed. In operation, the high-voltage power from the electrical connection box is converted into a low-voltage power by the series regulators in the electronic control units. Then, the so-converted, low-voltage is supplied to a plurality of electrical loads connected to respective electronic control units.
Meanwhile, recently, there has been developed a “high-voltage” vehicle using a voltage of 42V, which is loaded with a motor generator effective to reduce fuel consumption. However, if the above-mentioned power distribution apparatus is applied to such a high-voltage vehicle, then the power distribution apparatus exhibits a remarkably-deteriorated conversion efficiency and also a great heat generation. That is, if the vehicle adopts a power source of 14V and further a voltage for each load is equal to 5V, then the series regulators each has an efficiency of 35.7% [=(14−5)/14]. While, if the vehicle adopts a power source of 42V and further a voltage for each load is equal to 5V, the series regulator will have an efficiency of 11.9% [=(42−5)/42].
Although there might be supposed a method of adopting a switching regulator in place of the series regulator, it is impossible to prevent a battery from going flat because the switching regulator has a deteriorated conversion efficiency when the apparatus is operated under light load. In order to solve this problem, there has been proposed a system where all electronic control units that require stand-by currents (e.g. keyless unit) are respectively equipped with stand-by current suppliers. In this system, when an ignition switch is turned on, the power supply is accomplished by the switching regulators. On the other hand, when the ignition switch is turned off, the power supply is accomplished by the stand-by current suppliers. However, since this system requires expensive switching regulators for the respective electronic control units and also requires stand-by current suppliers for all of the electronic control units that require stand-by currents, the manufacturing cost for the same system is elevated excessively.
In connection, Japanese Patent Application Laid-open No. 10-84626 discloses another conventional power distributing apparatus where the electrical connection box is supplied with high-voltage power from the power source and also provided with a voltage converter which converts a high voltage into a low voltage (5V), so that the resultant low-voltage power is supplied to respective electronic control units. Owing to the provision of a single voltage converter, it is possible to construct the power distributing apparatus at low cost.
In this power distributing apparatus, however, there arises a problem of voltage drop in case of the power supply against electrical loads far from the voltage converter. In order to prevent such a faraway power supply, it is necessary to increase the number of voltage converters, causing the manufacturing cost to be elevated.
In addition, the voltage converter is required to meet requirements of the most severe electrical load in terms of converted voltage and temperature characteristics, causing the production cost of the apparatus to be elevated. Since the converter is apt to output with power fluctuations due to gain and loss in load currents, it is difficult to supply the plurality of loads with accurate powers.